The invention described herein relates to nuclear reactors and more particularly to an in-core emergency cooling system used to carry away heat generated in a reactor core in the event a major rupture occurs in the reactor main cooling system.
A nuclear reactor generally comprises a pressure vessel enclosing a reactor core. The core contains multiple fuel assemblies all of which include heat generating fissionable fuel elements while a certain number are provided with control rods movable in guide thimbles interspersed among the fuel elements. The degree of insertion of the control rods in the fuel assemblies determines and controls the amount of heat generated by the fuel elements. A liquid coolant circulated through the reactor core under high pressure, absorbs the generated heat and the thus heated coolant is then supplied to a steam generator which produces steam to power a steam turbine.
In the unlikely event of loss of liquid coolant resulting from rupture of a coolant supply or discharge pipe, the control rods mounted in the fuel assembly are automatically inserted to substantially stop the fission process. However, the residual heat in each fuel element or rod would be of a magnitude sufficient to adversely affect or severely damage the reactor core unless provision were made to positively effect its removal.
In recognition of this potential problem, the general design criteria established by the Atomic Energy Commission for the design and performance of nuclear reactors, requires that an emergency cooling system be coupled to each nuclear reactor to supply coolant thereto under conditions of a major break in the reactor main cooling piping and the consequent loss of coolant to the reactor components. All currently operational reactors therefore contain emergency cooling systems and in one well known design, large pressurized accumulators containing the needed emergency coolant, automatically discharges highly concentrated borated water into the reactor cooling system when the reactor system pressure drops below a certain pressure which indicates a major break in the piping. The emergency water is injected into the coolant inlet piping near the reactor inlet nozzles to assure direct delivery into the reactor core in need of a coolant liquid. This known system provides all the safeguards necessary if the major break occurs in an outlet pipe. However, some concern has been expressed as to the adequacy of this cooling system if the break occurs in one of the inlet pipes.
Because of this uncertainty, consideration has been given to an improved system which will positively supply coolant to the reactor core regardless of the location of a break in the main coolant system.